textproduct: Albany

WHAT HAS CHANGED

The coverage of showers and thunderstorms has increased for tomorrow, given the slower track of a low pressure system approaching from the northwest. Likewise, forecaster confidence in the greater coverage and probability of severe thunderstorms has also increased. Agreement in these thoughts has led the Storm Prediction Center has expanded the Slight Risk (Level 2 of 5) farther into the Mohawk and Upper- Hudson Valleys. A Marginal Risk (Level 1 of 5) remains in place for the Southern Adirondacks. The primary hazards remain damaging wind gusts (5-44% within 25 miles of any given point) large hail up to 1" in diameter (5-14% within 25 miles of any given point).

KEY MESSAGES

1) Isolated to scattered severe thunderstorms with damaging wind gusts and hail up to 1" in diameter are expected across the region tomorrow afternoon into tomorrow evening.

2) Additional periods of above-normal temperatures over the next seven days will bring at least minor to moderate risks of heat- related impacts.

DISCUSSION

KEY MESSAGE 1...

Tonight, a positively-tilted shortwave trough, whose axis extends from southwest Ontario into the Upper Midwest, will slide eastward and deepen as it reaches the eastern Great Lakes. The strengthening of this vertically stacking trough will trigger a deepening of the associated low at the surface, also tracking eastward through southern Canada. An initial surge of cyclonic vorticity advection associated with a shortwave embedded within the preceding zonal flow aloft will initiate some early showers tomorrow morning before deep atmospheric mixing scours out precipitation completely for the mid to late morning hours.

During these "dry" hours, breaks in cloud coverage amid southerly flow will allow instability to increase moderately as temperatures rise into the 70s across higher terrain and 80s to potentially low 90s in valley areas. Additionally, while we will be mixing rather deeply into the first half of the afternoon, persistent southerly flow will begin to increase dewpoints and subsequently instability. There is some uncertainty as to how moist we will get tomorrow due to the uncertainty in cloud coverage and how deep we will actually mix at times. But given the influx of moisture from the southerly flow and the quick showers that will moisten soils for some, the upper 50s to mid 60s dewpoints certainly seem reasonable.

By tomorrow afternoon, the aforementioned low will begin to move overhead as it settles into southern Quebec. A pre-frontal trough rounding the base of this low and tracking through the region tomorrow afternoon into tomorrow evening will ultimately drive convective development ahead of the impending cold front, which will track through the region tomorrow night into Sunday morning. The intersection of the combined forcing from the surface trough and the incoming shortwave aloft with the fairly unstable environment will be sufficient to drive an increased risk for severe thunderstorms tomorrow afternoon. 0-6km bulk shear vectors orienting roughly 45 degrees relative to the incoming surface trough at roughly 25 to 35 kt will support a discrete storm mode with some potential for stronger updrafts. This is also supported by steep mid-level lapse rates ranging from about 6.5 to 7 C/km. DCAPE values on the order of 800-1000 J/kg with inverted V profiles provide confidence that damaging wind gusts will be the greatest threat with any severe storms. However, large hail is also possible given decent cloud-layer shear and cooling temperatures aloft. The storm prediction center has expanded the Slight Risk (Level 2 of 5) to include additional portions of the Upper-Hudson and Mohawk Valleys while the Southern Adirondacks remain in a Marginal Risk (Level 1 of 5).

The timing of greatest threat for severe storms tomorrow falls between about 2 PM through 9 PM before the threat significantly decreases courtesy of the loss of daytime heating. And while there are no flooding concerns given our very dry period over the last several days, high PWATs are indicative of heavy downpours within any storms that develop tomorrow. Caution is advised for all those attending outdoor events or activities. Keep an eye to the sky and go indoors when you hear thunder.

KEY MESSAGE 2... While the aforementioned cold front will cool temperatures down for Sunday and Monday, we will still largely be above normal with temperatures largely in the 70s and 80s both days. And as we get further into next week, anomalously high geopotential heights (upper level heights 1-2 STDEVs above normal according to the latest NAEFS) will see temperatures surge into the 80s to 90s once again. At this time, the impacts for heat-related illness look to primarily be minor to moderate Sunday through Thursday, though some major impacts are beginning to slowly be introduced. We will continue to monitor trends going forward and provide additional messaging and products as confidence increases.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Through 18Z Saturday... VFR conditions are expected to prevail across all terminals through this TAF period. Westerly- northwesterly winds up to 5-10 kts will start off this period, before subsiding around 23Z-00Z tonight to calm and variable. This will persist through 12Z at KGFL, KPOU, and KPSF, with KALB expected to see winds starting to strengthen around 07Z. Winds will prevail out of the south/southwest on Saturday morning/early afternoon and gradually strengthen through the end of the TAF period, with gusts up to around 20 kts expected at KPOU and KPSF after 14Z-16Z.

SCT high-level cirrus will persist today into tomorrow morning at all terminals, with some scattered mid-level clouds beginning to develop Saturday morning. Cigs are expected to gradually lower throughout this period, but VFR cigs are expected to prevail. The only exception is KGFL, which could see cigs drop to MVFR after 14Z associated with scattered rain showers moving into the region around that time.

Outlook...

Saturday Night: High Operational Impact. Numerous SHRA...TSRA. Sunday: High Operational Impact. Breezy. Likely SHRA...TSRA. Sunday Night: Low Operational Impact. Breezy. NO SIG WX. Monday: No Operational Impact. NO SIG WX. Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Low Operational Impact. NO SIG WX.MA...None.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.